1. Field of the Invention
The present invention relates to a color image forming apparatus, and more specifically to a color image forming apparatus for carrying out calibration with a toner patch.
2. Description of the Related Art
Conventionally, since densities of obtained images in a color image printing apparatus vary due to changes of temperature and humidity of its operation environments and temporal degradation of components of an image forming system, a periodical adjustment processing of image forming conditions (calibration) is executed.
Generally, in the case of the color image forming apparatus of the electrophotography system, a toner patch for density detection is formed on an intermediate transfer body, the drum, or others with toner of each color, and the density of the toner patch is detected with the density detection sensor for the toner of each color so that a constant gray scale-density characteristic may be acquired. The image forming apparatus is configured so that a stable image may be obtained by executing a density control whereby a density detection result of the toner patch is fed back to process conditions, such as an exposure quantity and a development bias, and the conditions are altered.
When carrying out continuous printing with such an image forming apparatus, if the adjustment processing is waited until the printing is completed, a proper adjustment may not be able to be achieved. For this reason, there is proposed a technology of acquiring a more stable image by forming the toner patch for density detection between paper sheets printed successively on a photoconductor at the time of the continuous printing so that an adjustment processing may be possible even during printing (for example, refer to Japanese Patent Laid-Open No. 2001-199862). Moreover, there is proposed a configuration that enables a half tone processing for each object to be performed even for an image input for which a definition of the half tone processing changes for every object (for example, refer to Japanese Patent Laid-Open No. 2009-358756).
However, in order to realize further higher quality of image with the technology whereby the toner patch is formed between paper sheets at the time of the continuous printing that was explained in the paragraph of BACKGROUND ART and a more stable image is obtained, a configuration of switching the half tone processing for every object is needed and consequently kinds of half tones increase. As a result, it is necessary to increase the kinds of patches required for a density adjustment, and therefore this configuration poses a problem that a space between paper sheets must be set more by that increment.
The present invention is made in view of the above-mentioned problem, and aimed at providing a capability of extending an area where the toner patch can be formed at the time of the continuous printing as much as possible, so that the necessary density adjustment is achieved without extending the space between paper sheets printed successively.